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Time Scales of Land Surface Hydrology

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  • 1 Department of Atmospheric Sciences, The University of Arizona, Tucson, Arizona, and Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 2 Department of Atmospheric Sciences, The University of Arizona, Tucson, Arizona
  • 3 Department of Mathematics and Statistics, University of Alberta, Edmonton, Alberta, Canada
  • 4 Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 5 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
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Abstract

This paper intends to investigate the time scales of land surface hydrology and enhance the understanding of the hydrological cycle between the atmosphere, vegetation, and soil. A three-layer model for land surface hydrology is developed to study the temporal variation and vertical structure of water reservoirs in the vegetation–soil system in response to precipitation forcing. The model is an extension of the existing one-layer bucket model. A new time scale is derived, and it better represents the response time scale of soil moisture in the root zone than the previously derived inherent time scale (i.e., the ratio of the field capacity to the potential evaporation). It is found that different water reservoirs of the vegetation–soil system have different time scales. Precipitation forcing is mainly concentrated on short time scales with small low-frequency components, but it can cause long time-scale disturbances in the soil moisture of root zone. This time scale increases with soil depth, but it can be reduced significantly under wetter conditions. Although the time scale of total water content in the vertical column in the three-layer model is similar to that of the one-layer bucket model, the time scale of evapotranspiration is very different. This suggests the need to consider the vertical structure in land surface hydrology reservoirs and in climate study.

Corresponding author address: Aihui Wang, Dept. of Atmospheric Sciences, 1118 E. 4th St., P.O. Box 210081, The University of Arizona, Tucson, AZ 85721. Email: ahwang@atmo.arizona.edu

Abstract

This paper intends to investigate the time scales of land surface hydrology and enhance the understanding of the hydrological cycle between the atmosphere, vegetation, and soil. A three-layer model for land surface hydrology is developed to study the temporal variation and vertical structure of water reservoirs in the vegetation–soil system in response to precipitation forcing. The model is an extension of the existing one-layer bucket model. A new time scale is derived, and it better represents the response time scale of soil moisture in the root zone than the previously derived inherent time scale (i.e., the ratio of the field capacity to the potential evaporation). It is found that different water reservoirs of the vegetation–soil system have different time scales. Precipitation forcing is mainly concentrated on short time scales with small low-frequency components, but it can cause long time-scale disturbances in the soil moisture of root zone. This time scale increases with soil depth, but it can be reduced significantly under wetter conditions. Although the time scale of total water content in the vertical column in the three-layer model is similar to that of the one-layer bucket model, the time scale of evapotranspiration is very different. This suggests the need to consider the vertical structure in land surface hydrology reservoirs and in climate study.

Corresponding author address: Aihui Wang, Dept. of Atmospheric Sciences, 1118 E. 4th St., P.O. Box 210081, The University of Arizona, Tucson, AZ 85721. Email: ahwang@atmo.arizona.edu

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